Although the subject invention may have other uses, it is particularly suitable for use in a marine steering system. A marine steering system in a boat typically includes a double-acting steering cylinder connected to the rudder of the boat and supplied hydraulic fluid through two lines connected to opposite ends of the cylinder and extending to a manually operated steering pump typically connected to a steering wheel which is manually rotated in opposite steering directions.
Such steering systems frequently also include an automatic pilot which detects the course of the marine vessel and makes course corrections by feeding signals to drive an auxiliary hydraulic fluid pump which is also connected to the hydraulic steering cylnder. The auxiliary pumps typically used in such systems have low volumetric efficiency, high internal slippage, and require check valves to isolate the pump from the remainder of the manually actuated steering assembly.